Multicast and broadcast are techniques for transferring data from one data source to multiple destinations. In a traditional mobile network, the Cell Broadcast Service (CBS) allows low bit-rate data to be transferred to all users via a shared broadcasting channel of a cell, which is categorized as a message service. At present, voice and message services can not satisfy people's need for mobile communications. Along with the rapid development of the Internet, there is emerging a great deal of multimedia services, some applications of which require that multiple users are able to receive the same data at the same time, e.g. video on demand, video cast, video conference, network-based education, and interactive video games. Compared with conventional data, these multimedia services are featured with large data flow, long time duration, and high sensitivity to time delay. The existing IP multicast techniques make it possible to implement these multimedia services in the form of multicast or broadcast on cabled IP networks. However, as mobile networks have special network architectures, functional entities, and radio interfaces, which are all different from those of cabled IP network, existing IP multicast techniques are not applicable to mobile networks.
In order to make efficient use of resources of mobile networks, the WCDMA/GSM global standardization organization, 3GPP, has put forward the Multimedia Broadcast/Multicast Service (MBMS), designed to provide point to point services of transferring data from one data source to multiple users in mobile networks so as to share network resources and improve the utility rate of network resources, especially the utility rate of resources of radio interfaces. The MBMS defined by 3GPP can multicast and broadcast not only low-rate text messages but also high-rate multimedia services, which is no doubt in accordance with the trend of future development of mobile data.
A reference model of the architecture of an MBMS system is shown in FIG. 1. In order to support the MBMS, a new mobile functional network entity—Broadcast Multicast-Service Center (BM-SC) is added to a mobile network, which is the entrance of content providers and is used in authorizing and initiating an MBMS bearer service as well as transferring MBMS contents according to a pre-defined schedule.
In addition, functional entities such as UEs, the UMTS Terrestrial Radio Access Network (UTRAN), the GSM Edge Radio Access Network (GERAN), the Serving GPRS Support Node (SGSN), and the GPRS Gateway Support Node (GGSN), are enhanced to incorporate functions relevant with the MBMS.
The MBMS includes a multicast mode and a broadcast mode. In the multicast mode, it is necessary for a user to subscribe to a corresponding multicast group, implement service activation, and generate corresponding accounting information. As there is a difference between the multicast mode and the broadcast mode in service demands, the service procedures of them are different.
There are two modes for transferring the MBMS between the UTRAN and UEs: a Point to Multipoint (PTM) mode and a Point to Point (PTP) mode. In the PTM mode, same data are sent via an MBMS PTM Traffic Channel (MTCH), and may be received by all UEs which have joined the multicast service group or are interested in the broadcast service. In the PTP mode, data are sent via a Dedicated Traffic Channel (DTCH), and can be received by only one corresponding UE.
The complete procedure for a UE receiving a particular MBMS broadcast service is shown in FIG. 2, while the complete procedure for a UE receiving a particular MBMS multicast service is shown in FIG. 3. As seen from FIG. 3, the specific steps for a UE receiving a particular MBMS multicast service includes:                1. Subscription: Setting up a connection between a UE and a service provider;        2. Service announcement: Notifying the UE of information related with the MBMS;        3. Joining: the UE informing the network that it is ready to receive the MBMS;        4. Session Start: the BM-SC getting prepared for data transfer;        5. MBMS notification: the RNC (Radio Network Controller) notifying the UE of the transfer of MBMS multicast data;        6. Data transfer;        7. Session Stop: the BM-SC will no longer transfer data, and therefore bearer resources can be released;        8. Leaving: the UE is no longer a member of the MBMS multicast group.        
First, the features and relevant information of the MBMS PTM Control Channel (MCCH) are described below.
The MCCH information is transferred based on a fixed scheduling method. The UTRAN repeatedly transfers the MCCH information to improve the stability. The MCCH scheduling is consistent for all services.
The entire MCCH information is periodically transferred based on a “Repetition period”. “Modification period” is defined as an integral multiple of “Repetition period”. MBMS Access Information is periodically transferred based on an “access information period”. Meanwhile, “Repetition period” is also an integral multiple of “access information period”.
The MCCH information is categorized into critical information and non-critical information. The critical information includes MBMS NEIGHBORING CELL INFORMATION, MBMS SERVICE INFORMATION, and MBMS RADIO BEARER INFORMATION. The non-critical information includes MBMS ACCESS INFORMATION. The critical information can not be changed during each Modification period while the access information may be changed at any time. The scheduling of MCCH information is shown in FIG. 4.
As can be seen from FIG. 4, the critical information is periodically transferred through the MCCH according to a Repetition period (RP) and a Modification period (MP), and the critical information can not be changed within an MP. The non-critical information, however, is transferred according to an access period, and the access information may be changed in an access period.
Before Step 4 of Session Start in FIG. 3 and possible procedure of counting, in order to save system resources, the UTRAN will request a UE to re-select a preferred frequency layer, and it is likely that the MBMS is transferred only on the frequency layer. Information of the preferred frequency layer is transferred to the user by the network via the MCCH, and the procedure is referred to Frequency Layer Convergence (FLC). By the procedure, the UTRAN can make all UEs within a particular area converge to one frequency layer. Each MBMS has a preferred layer. As the preferred layer is determined by UTRAN, this is an issue of Radio Resource Management (RRM). Therefore, identical services in different areas may have different preferred layers, and different services in the same area may have different preferred layers as well.
At the beginning of Step 4 of Session Start in FIG. 3, before the FLC procedure, the UTRAN may also make a Counting operation to decide which radio bearer mode of air interface is to be used. In an MBMS system, there are two radio bearer modes, the PTP and PTM. Simply speaking, the PTP means that MBMS is transferred to a UE via a dedicated channel in the network, while the PTM means that the MBMS is transferred to a UE via a public channel.
At Step 7 of Session Stop in FIG. 3, as an FLC procedure may have been performed, many users that have received a particular MBMS may have re-selected a particular preferred frequency layer. If so many users conduct a non-MBMS service, a severe congestion in the system will be however caused. That is why another procedure referred to Frequency Layer Dispersion (FLD) is designed in the MBMS system. By this procedure, it is possible for the UTRAN to re-disperse the users to different frequencies so as to reduce the number of users on the original frequency layer and mitigate the congestion in the network. The network will send an instruction on whether there is an FLD operation to users via the MCCH.
In the prior art, the procedure of the FLD operation has only considered the situation that the UE has joined one MBMS and an FLD operation is needed when the session of the MBMS is end. However, no specific procedure has been considered for the situation when there are simultaneously multiple MBMSs.
As no specific procedure of implementing the FLD operation is defined after the FLD is introduced into solutions in the prior art, the user will consider the instruction and carry out responding actions if the network gives the instruction of the FLD operation. In prior art, only the situation that one MBMS has the FLD operation is considered, which however is incomplete in that one UE may join many MBMSs which are providing or will be provided in the network, and are likely to carry on same or different operations which can not be treated as the same, such as the FLC, FLD, counting etc.
If the UE is constrained with the capacity and is impossible to receive so many services, the need for processing based on service priority will arise, i.e. the user has to decide which service is the most desired one and which one is not wanted at present.
Under the circumstances as described above, if the user just follows the instruction of the network in carrying out the FLD operation without considering other services, a severe problem will occur and the user is likely to make selection of frequency layer twice, or can not receive the desired service.
For example, if the UE is in a cell of Frequency 1 and at this time, a Service A and a Service B are provided in the cell (for the UE, the Service A has a higher priority than the Service B). If the Service A is provided in the local cell while the Service B is provided on another frequency layer, the network will instruct the UE to carry out the FLD operation for the Service B; however, the UE will prefer to receive the Service A at this time rather than carry out the FLD operation relevant to the Service B. The solution in the prior art, however, gives no description to the settlement of such a conflict.
The pre-condition for a user carrying out the FLC operation is to completely receive the information of the MBMS provided by the local cell so that the desire of the user could be reflected and relevant operations could be correctly performed. This, however, is not defined in the existing solutions either.
Therefore, there is a major drawback during the flow of prior art, and the user is likely to be unable to get a complete picture of the services provided in the local cell so that the wrong operations may be made, e.g. a user is possible to make such a mistake as first performing the FLD operation and then FLC operation, and waste in power and time is caused by repeated frequency switching.